Pneumatic fastener driving machine



Aug. 17, 1965 c. v. LE SAGE PNEUMATIC FASTENER DRIVING MACHINE 4Sheets-Sheet 1 Filed July 23, 1963 INVENTOR.

C(AIPf/Vf V. A JAG A'- Aug. 17, 1965 c. v. LE SAGE PNEUMATIC FASTENERDRIVING MACHINE 4 Sheets-Sheet 2 Filed July 23, 1963 0 a ll R. Q 6 w 6 mI 4 @im 5 1M 6 6 2, 0 62 3 M 02 2 a 4 8 3 1| 8 6 lv 9 3 L: M v mk M V.QM i. Q M a 3 5 O 3 1965 c. v. LE SAGE 3,200,716

PNEUMATIC FASTENER DRIVING MACHINE Filed July 23, 1963 4 Sheets-Sheet 4'TQEELQ United States Patent 3,260,716 PNEUMATIQ FASTENER DRIVENGMACHINE Clarence V. Le Sagcfllos Angeles, Calil-Z, assignor to BerryCalifornia Corporation, Los Angeles, Elalif, a corporation of CaliforniaFiled July 23, 1963, der. No. 296,964 12 Qlaims. (til. 91-461) Thisinvention relates to improvements in fastener driving machines andappliances and more particularly to an improved piston driven implementactuated by pres sure fluid, for example by air pressure.

Whle the present invention is herein illustrated and described in theform of a portable fastener driving implement, specifically a gun-typepneumatically operated stapler, it is to be understood that it may beembodied in other structures such as a stationary machine mounted on asuitable base. The implement disclosed herein may be employed in manydifferent industries for fastening together various articles withstaples, nails or corrugated fasteners.

An object of the present invention is to provide a machine of the typeindicated of simplified construction and improved efficiency which has arelatively high power-toweight ratio to facilitate use as a portableimplement.

A more particular object of the invention is to provide in a machine ofthe above character an improved valve for controlling the admittanceand/ or exhaust of pressure fluid to the main cylinder which is entirelypressure fluid actuated so as to eliminate the need for a spring in thevalve mechanism.

Other objects, features and advantages of the present invention willbecome apparent from the following description taken with theaccompanying drawings which by way of example illustrate a preferredembodiment of the invention wherein:

FIG. 1 is a fragmentary vertical center section of a portable guntypepneumatic fastener driving implement embodying the invention, the noseand magazine portions thereof being shown in elevation and the workingparts being shown in position ready for actuation of the piston on adriving stroke.

FIG. 2 is a similar fragmentary vertical center section of the implementbut showing the piston at the end of its driving stroke, the maincylinder valve open, and the associated exhaust valve closed.

FIGS. 3 and 4 are sectional views taken respectively on the lines 3-3and l of FIG. 2.

FIG. 5 is an enlarged view of a portion of FIG. 1 illustrating in partthe trigger valve and cylinder valve mechanisms.

FIG. 6 is still a further enlarged view of a portion of FIG. 5illustrating the valve seating structure of the cylinder valve.

FIG. 7 is a sectional view taken on the line 7-7 of FIG. 1.

FIG. 8 is a sectional view taken on the line 8-8 of FIG. 1.

FIG. 9 is a vertical center section of the body casing of the implementwith the working parts omitted.

FIGS. 10 and 11 are enlarged views of the upper portions of FIGS. 1 and2 respectively.

As illustrated in FIGS. 1 and 9, the pneumatic stapler of the inventionhas a generally pistol-shaped die cast 3 ,2 0d,? 1 6 Patented Aug. 17,1965 body comprising a barrel casing Ill and a hollow handle 12. Casingill contains the fastener driving mechanism and surmounts the forwardend of a magazine 14 which may be of known construction for containingwire staples 16 or other types of fasteners. The forward end of magazine14 is fastened to the lower end of casing It, by a nose assembly 13having a guideway Ztl in which a staple driving blade 22 reciprocates.Handle 12 (FIG. 9) is shaped so that it may be grasped in the hand fortransporting the stapler and holding nose 1%) against the work.

As best seen in FIG. 9, casing Ill is formed with three progressivelylarger diameter co-axial cylinders comprising a forward cylinder 24, amain cylinder 26 and a valve cylinder 23. The upper portion of casing 10encircling cylinder 26 is cored out to provide an annular pressure airstorage chamber 3t) which is open around the upper end thereof, exceptfor four connecting webs 32, to an annular groove 34 encircling theupper end of cylinder 25. Chamber 31) on the handle side of easing 1t)communicates via a relatively large forked passage 35 (FIG. 4-) withanother air chamber 35 formed within handle 12. Compressed air or otherpressure fluid is supplied .to chamber 36 by connecting a suitable hose(not shown) to an inlet 37 (FIG. 9) at the outer end of handle 12, theother end of the hose being connected to a suitable source of compressedair. Due to the relatively unrestricted communication between chambers36 and 30, constant pressure is maintained in both chambers and togetherthey provide a pressure air storage reservoir having a volumetriccapacity approximately three times the displacement of adifferential-type driving piston 38 (FIGS. 1 and 2). which reciprocatesin cylinders 24 and 26.

Piston 38 has a cylindrical lower end 40 (FIG. 8) which has a slidingseal fit in cylinder 24, and a cylindrical upper end comprising acup-shaped crown 41 (FIGS. 2 and 4) having a flange 42 of largerdiameter than lower end 44) which has a sliding seal fit in cylinder 26.

Lower end 4t) of piston 38 carries an adaptor 46 (FIG. 1) which isattached thereto by screws 48 threaded into piston 38, blade 22 beingsuitably secured to adaptor 46.

A valve assemby 52 (FIGS. 2, 10 and 11) for controlling admittance toand exhaust of air from main cylinder 26 comprises a piston 54, a tube56 and a hex nut Valve piston 54 is secured to tube 5:? by nut 58threaded on the lower end of tube 56. Valve piston 54 reciprocates incylinder 28. A sleeve 6t) is fixed in casing Itl between a shoulder 62(FIGS. 1 and 10) at the upper end of cylinder 28 and an end cap 64removably attached to the upper end of the casing. Tube 56 slides insleeve 66.

Valve assembly 52 is pneumatically actuated to re ciprocate between theposition thereof shown in FIGS. 1 and 10 and the position shown in FIGS.2 and 11 for controlling admission of pressure air from chamber 30 to.cylinder 26 and for controlling exhaust of spent pres sure air fromcylinder 26 to atmosphere. Valve piston 54 has a hard rubber seal ring66 (FIG. 3) bonded to the underside thereof which has a tapered rimportion '70 (V-shaped in cross section, FIG. 6). Rim '79 seats on theupper end face 63 of cylinder 25 in the cylinder-closing position ofvalve assembly 52 and provides high contact pressure engagement and alsospaces a radial face 72 of valve piston 54 from face 68. Hence, arelatively small working surface (face '72 and rim 7t?) of valve piston54 is constantly exposed to pressure fluid in chamber 34 to provide aforce acting upwardly on valve piston 54 tending to unseat rim '70 ofring 65.

Seal ring as also has a fiat annular face 74 (PEG. 6) against which theend face of crown flange 42 abuts in the raised position of piston 38.Ring face 74 is separated by an annular groove 76 from rim 7%.

Valve assembly 52 is normally maintained in cylinder closing position bypressure air admitted from chamber 39 via a constantly open restrictedpassage 89 in valve piston 54 (FIGS. and to a chamber 32 formed betweenvalve piston 54 and sleeve W. The working area on the upper side ofvalve 54 exposed to air pressure in chamber 82 is much larger than thearea of face 72 and rim and therefore when the pressure in chamber 82equals that in chamber 3%, the force holding ring 66 seated greatlyexceeds the force tending to unseat it. As seen by comparing FIGS. 10and 11, a counterbore 83 communicates with restricted passage 36 andwith groove 34 in all positions of valve piston 54.

The trigger mechanism of the pneumatic stapler controls communicationbetween chamber 82 and the outside atmosphere and comprises a trigger 84(FIGS. 1 and 2) pivoted at 86 to casing 10, a hexagonal trigger rod 88contacting trigger 84 at the lower end thereof, an outlet valve assemblyhit at the upper end of rod 83 and an outlet passage 92 leading fromchamber 82 to a port 93 in the side of a valve casing 94 of valveassembly l t). Rod 8% slides in a circular bore M in an internal portion9'7 of the die casing 1t? (KG. 3, 4 and d) which extends through chamberSt). Valve casing 94 (FIG. 5) is press fitted in a counterbore 98 (FIG.9) for retention by cap 64. The upper end of rod 88 has a stem res whichextends axially therefrom through a port 192 in casing 94 and carries aball check valve 104 for closing port 102. A coil spring 1% biases valve1M to its normally closed position. When valve W4 is unseated, pressureair escapes from chamber 82 via passage 92 into casing 94, past valve164 and through port 102 and the clearance space between hex rod 88 andits bore 96, as illustrated by the arrows in FIG. 11.

Exhaust of spent pressure air from main cylinder 26 is controlled by theexhaust valve structure at the upper end of tube 56 of valve assembly52. A radial end flange of tube 56 carries a hard rubber seal ring 112;which, in the cylinder-opening position of valve assembly 52 (FIGS. 2and 11), seats against a flat recessed surface 114 of cap 64. As bestseen in the enlarged views of FIGS. 5 and 10, ring 1112 has a taperedrim 116 .(V-shaped in cross section) which insures high unit contactpressure by ring 112 against surface 114,. Rim 116 also spaces theannular surface 118 of flange 11!) (FIG. 5) from cap surface 114 in theseated position of seat ring 112 (FIG. 2). The upper inner end of tube56 has a beveled surface 12d radially inwardly of ring 112 which is alsospaced from cap surface 11 when ring 112 is seated thereagainst (FIG.11). Due to this spacing, the portion of surface 113 within ring 112 andbeveled surface 120 are not cut 03 from exposure to main cylinder airpressure via bore 122 of tube 56 when ring 112 is seated against surface114. However, the working area consisting of surfaces 118 (within ring112) and 120 tending to unseat ring 112 is less than the eflectiveworking area of the underside of valve assembly 52 which is also exposedto main cylinder air pressure when it is in the position of FIG. 2.Hence, the net force acting on valve assembly '52 is in an upwarddirection (FIG. 2) and is sufficient to hold ring rim'lld tightly seatedagainst cap surface 114. In its seated position, ring 112 closescommunication between bore 122 leading to main cylinder 26 and a pair ofexhaust passages 124 and 126 (FIG. 7) provided in cap 64 which lead toatmosphere.

Driving piston 38 is normally maintained in the retracted position ofFIG. 1 by air at line pressure acting on the relatively small effectiveworking area of the underside of flange 42 of piston crown 41. Thisworking area is equal to the cross-sectional area of cylinder 26 minusthat of cylinder 24-, and is approximately 11 percent of the eflectiveworking area of the upper side of piston 31$. However, when valve piston54 is closed and exhaust valve portion lid is open, the upper side ofpiston 38 is exposed only to atmospheric pressure in cylinder 26. Theannular space 127 between cylinder 26 and piston 33 intermediate theopposite ends of the piston comprises an air return chamber which is inconstant communication with pressure air chamber 30 via an air returnpassage 130 which communicates at its lower end with cylinder 26 via aflaring outlet 132. (FIGS. 4 and 9) which merges into an annular groove13d encircling the lower end of cylinder 26. The upper end of passage 1%communicates with chamber 30 via a port 135. It is to be noted that portextends radially inwardly so as to direct the air which is forced fromair return chamber 127 upwardly via passage 13th (as a result ofdownward movement of piston 38 on its driving stroke) radially inwardlyacross end face 6% of cylinder 26 into the cylinder to therebysupplement incoming pressure air from reservoir 30 for driving piston 38on its working stroke.

Piston 33 may be made of lightweight metal but is preferably injectionmolded from a suitable moldable plastic, such as that known by thetrademark Lexan and sold by General Electric Company. As shown in FIGS.2 and 8, crown 41 and lower end 4% of piston 30 form the oppositeimperforate cylindrical ends of piston 38, and these ends areinterconnected by four axially extending ribs 1% integrally joined toone another along the central axis of piston 33 and extending radiallyoutward therefrom. Due to the relatively low 7 mass of piston 38compared to that of the remaining structure of the implement, the recoileffect produced by the impact of the piston against bumper at the end ofits working'stroke is reduced to a minimum.

Operation Assuming that magazine 14 is loaded with staples 16 and thathandle reservoir 36 is connected by a length of hose to a suitablesource of compressed air, handle 12 may be grasped in one hand fortransporting the stapler to the work. Normally, piston 38 will be in itsuppermost position (FIG. 1) with blade 22 raised above the top of theforemost staple 16 disposed in guideway 29. Piston 38 is normallysustained in its raised position by pressure air admitted beneath crown42 via passage 1% communicating with the interconnected storagereservoirs 3t and 36. Valve assembly 52 will normally be in itslowermost position (FIG. 1) wherein rim 70 (FIG. 6) seats on face es ofcylinder 26 to thereby close the upper end of cylinder 26 and isolatethe upper side of piston 38 from pressure air in reservoir 3t), 36, andwherein valve portion lid is open so that only atmospheric pressure isacting downwardly on the piston. Valve 52 is sustained in itscylinder-closing position by air at line pressure admitted fromreservoir 39 to chamer 82 via passages 80, 33, valve 1G4- being closedat this time.

It is to be understood that when piston 38 and valve assembly 52 are intheir above-described positions, valve assembly 52 serves as an upperstop for piston 33 (FIG. 6). Since the downwardly effective working areaon the upper side of valve piston 54 exposed to line pressure in chamber82 (FIGS. 5, 7) is many times the upwardly elfective working area ofpiston 38 between crown flange 42 and lower end 49 thereof likewiseexposed to line pressure in air return chamber 127, the force urgingpiston 33 upwardly against valve piston 54 is not sufficient to unseatit. Under the aforementioned conditions, the stapler may be positionedabove the work and between rim 7t) and the cylinder end face 68.

applied thereto by holding its nose 18 thereagainst; or

in other cases the stapler may be tilted and placed in position with thenose against a vertical, inclined or overhead work surface.

After the stapler has been applied to the work, the staple-driving phaseof operationis initiated by squeezing trigger 84 upwardly to theposition of FIG. 2, thereby lifting valve 164 from its seatand openingcommunication between chamber 32 and atmosphere via' passage 92, port192 and passage 96. The lower end of passage 96 communicates directlywith atmosphere. Although chamber 82 is constantly being supplied withair at line pressure via restricted orifice 30, the passages 92, 102 and96 have a much larger flow capacity than orifice 80 and hence air isbled from chamber $2 much faster than it is replenished. When the airpressure in chamber 82 has dropped sufficiently to lower the forceacting downwardly on valve piston 54 (as viewed in FIG. 1) to less thanthe forces acting upwardly on surface '72 and rim ill thereof (FIG. 6),valve piston 54 becomes unbalanced and begins to move upwardly, therebybreaking the seal This exposes the entire working area of the undersideof valve assembly 52 to compressed air as it rushes into cylinder 26from storage chamber 34 thereby rapidly increasing the total forceacting upwardly on valve assembly 52 so that it snaps upwardly andforces ring 112 against surface 114 to close off cylinder 26 fromexhaust passages 124, 126.

The quick cylinder-opening action of valve 52 provides a dumping effect,e.g., it quickly exposes or opens the entire upper end of cylinder 26 sothat a large volume of compressed air from reservoir 30 is rapidlyadmitted to cylinder 26 to drive piston 38 rapidly downwardon itsdriving stroke until it strikes a bumper 14-0 retained by nosepiece It;at the lower end of cylinder 24- (FIG. 2). Blade 22 is thus driven bypiston 33 with high impact force for separating the foremost staple fromthe stick of staples 16 and driving it via guideway 20 into the work.The air in cylinder 24 below the lower end 49 of the piston is expelledto atmosphere via a port 142 in nosepiece 13 (FIG. 2). Piston 33 remainsin its lowermost position (FIG. 2) as long as trigger valve 164 is heldopen by the operator, usually only a matter of a second or so, duringwhich time there is a constant though small less of compressed air fromreservoir 3h, .56 to atmosphere via the orifice 89, chamber 82 andpassages 92 and 96.

In the second or blade-return phase of operation of the pneumaticstapler, piston 3:8 and valve assembly 52 are returned from theirrespective positions shown in FIG. 2 to their normal or retractedpositions shown in FIG. 1. When trigger 8.4 is released, spring 1%closes valve 104- so that compressed air entering chamber 82 via orificetill no longer can escape to atmosphere and consequently pressure buildsup in chamber 82 until it equals the pressure existing in chamber 3t},e.g., the nominal supply line pressure. As the air pressure in chamber82 approaches line pressure, the force acting downwardly on valveassembly 52 increases until it balances and then exceeds the forceacting upwardly thereon. This downward unbalancing occurs prior topressure being equalized in chambers fail and 32 since the effectiveworking area (acting downwardly) of exhaust valve surfaces 118, 120exposed to line pressure in cylinder 26 via bore 122 plus the workingarea of valve piston 54 exposed to pressure in chamber 82 exceeds theoppositely or upwardly acting working area on the underside of valveassembly 52 exposed to line pressure in cylinder 26 as viewed in FIG. 1or 2. As soon as the net force acting on valve assembly 52 is in thedownward direction, valve 52 begins to .move downwardly, therebyunseating ring 112 and thus opening communication between cylinder26 andatmosphere via exhaust passages 122, 124, 12s. This causes an immediateand severe reduction of air pressure in cylinder 26 so that valve piston5.4 is urged downwardly as viewed in FIG. 2 towards its cylinder-closingposition of FIG. 1 with greater force by the pressure air in chamber 82.Also, when the pressure in cylinder 26 above piston 38 drops as a resultof the exhaust valve portion being opened, the pres sure air in space127 beneath piston crown 4-1 provides sufiicient force to drive piston38 upwardly on its return stroke until it strikes ring 66 of valvepiston 54, the latter having seated in cylinder-closing position by thistime.

From the foregoing, it will now be apparent that one important featureof the invention is the provision of the poppet valve assembly 52 whichfunctions in the dual role of both an air pressure inlet control valveand an exhaust control valve solely in response to fluid pressuresacting thereon under the remote control of trigger valve 194. Valvepiston 5 controls the inlet or supply of pressure air to cylinder 26,and exhaust valve portion ill-ll of tube 56 controls communicationbetween the cylinder 26 above piston 3% with atmosphere. As valveassembly 52 rises to admit pressure air to cylinder 26 above piston 3%,it simultaneously closes the exhaust ports 124,, 126 through which thecylinder as above piston 38 communicates with atmosphere, and viceversa. This arrangement thus eliminates the need for a return spring toinitiate unseating movement of exhaust valve portion lit). This not onlyreduces cost and increases reliability, but also eliminates theundesirable effect or t e biasing force of such a spring which tends toretard upward movement of the valve assembly and thereby negate to someextent the aforementioned desired dumping effect.

It is also to be noted that valve assembly 52 operates in the manner ofa poppet valve in performing its dual function as a pressure inlet valveand as an exhaust valve for spent pressure air. This type of valve isadvantageous over a slide-type valve since a poppet valve does notrequire tolerances as close as those required by slide valves and doesnot suffer from wear to the same extent. Valve assembly 52 alsosimplifies the exhaust passageway structure by uniting tube 56 withvalve piston 54 so that tube 56 serves as both an exhaust conduit andvalve for closing the conduit. The relatively large bore 122 of tube aspermits rapid exhaust of spent pressure air from the space above piston35% in cylinder 26 so that the return stroke of the piston is relativelyrapid. This in turn reduces the total cycle time of the gun and thusincreases the maximum numberof fasteners which can be driven by theimplement during a given unit of time.

Several other features of the present invention also contribute to theresult of developing maximum power in the working stroke of the pistonwhile economizing motive pressure air during this phase of operation.The theoretically ideal mechanism would provide exposure of the fullworking area of the upper side of piston 33 to line pressure at thebeginning of its working stroke and maintenance of this pressure thereonthroughout the working stroke in order to produce the maximum power fordriving a staple into the work. Although this ideal condition can onlybe approximated in a practical pneumatic stapler, another feature of thepresent invention which contributes to better approximation of the idealsituation is the valve seat structure best seen in FIG. 6. The pointedrim '70 (as viewed in section) of ring 66 which has a circular edgecontact with face as reduces flow resistance through the initial orificeprovided when it is unseated from the end face 68 of cylinder 26 so thatpressure air quickly enters annular groove 76 to increase the forceacting upwardly on valve assembly 52.

Another feature which contributes to rapid unseating of valve piston 54and operating efliciency is the provision of co-operative contours onthe upper end of piston 38 and on the portion of valve assembly 52received therein. The cup-shaped crown 41 at the upper end of piston 38provides a well 14 5- in which not 53 and the lower portion of tube 56of valve assembly 52 nest when piston 38 and valve assemlby 52 are intheir respective positions shown in FIG. 1. An integral tubular portion146 of piston 38 extends axially upwardly therefrom and has a closeclearance fit in tube 56 for restricting flow of pressure air from well144 into bore 122 during the initial opening movement of valve piston 54in the first phase of operation. This causes air pressure to build uprapidly in the annular space between crown 41 and valve assembly 52 andreduces loss of pressure to atmosphere via bore 122 and cap exhaustpassages 124, 126. Since pressure air is at this time being bled fromchamber 82 whereas the pressure air beneath piston 33 is substantiallyat line pressure, valve 54 accelerates at a faster rate than piston 38immediately after valve piston 54 is unseated. Therefore, tubularextension 146 will remain relatively stationary during movement of valveassembly 52 upwardly and hence will continue to restrict communicationbetween well 144 and bore 122 substantially until exhaust valve lid isseated. Loss of motive pressure air via the exhaust passages toatmosphere is thus substantially reduced during the critical period atthe beginning of the working stroke of the piston.

A further feature contributing to economical utilization of pressurefluid is the provision of air return passage 13% and the radiallyinwardly directed outlet 135 thereof which, as shown in FIG. 2, directsthe pressure air trapped in space 127 beneath piston crown 4-1 directlyinto cylinder 26. Since piston 33 is a high ratio differential piston(e.g., the downwardly effective area on the upper side of piston 38 isabout nine times the oppositely upwardly effective Working area ofpiston 38 exposed to pressure in air return chamber 127), a pressuremultiplication effect is obtained which causes pressure air to issuefrom outlet 135 in a high velocity, radially inwardly directed streamwhich impinges on valve assembly 52 and is then deflected into cylinder26 to augment incoming pressure air from reservoir 30.

In addition to the aforementioned features of the fastener drivingimplement of the invention, it will now be seen that the improvedstructural organization of the above-described parts of the implementrepresents a compact arrangement and an efficient design from amanufacturing as well as an operational standpoint since the parts areadapted to be readily made and assembled by mass production techniques.Also, the number of parts is reduced to a minimum.

I claim:

1. In a fastener-applying machine the combination comprising a reservoirfor pressure fluid, a cylinder having an inlet port communicating withsaid reservoir, a piston reciprocable in said cylinder, a valve movableto open and'close said inlet port, an exhaust tube movable with saidinlet valve and adapted to communicate at opposite ends thereofrespectively with said cylinder and with atmosphere, means for slidablyguiding said tube and for opening and closing the atmosphere end of saidtube in response respectively to closing and opening movement of saidinlet valve, said last-mentioned means comprising a sleeve and a closurecap defining an exhaust chamber therebetween communicating withatmosphere, said cap defining an end wall of said exhaust chamberdisposed perpendicular to the axis of said tube against which saidatmosphere end'of the tube axially abuts to close the same, said tubebeing slidably supported in said sleeve with said atmosphere end of saidtube projecting axially therefrom into said exhaust chamber in radiallyspaced relationfrom the radially surrounding wall of said exhaustchamber, said tube having a pressure surface exposed via the interior ofsaid tube to pressure fluid in the cylinder when said tube is closed anddisposed to develop an opening force on said tube, said inlet valvehaving a pressure surface exposed to reservoir pressure fluid forholding said inlet valve in open position with a force greater than thatdeveloped by said tube pressure surface,

8 and means for developing a force on said inlet valve additive to theforce of cylinder pressure fluid acting on said tube pressure surface tothereby initiate opening movement of said tube and closing movement ofsaid inlet valve.

2. The combination set forth in claim 1 wherein said inlet valve andsaid piston are disposed co-axially and move oppositely relative to oneanother between positions adjacent and remote from one another, saidpiston and said inlet valve having means movable therewith adapted totelescopically overlap in the direction of movement thereof in a regionspaced inwardly of said cylinder inlet port to thereby restrict flow ofpressure fluid from said reservoir into said exhaust tube when saidpiston and inlet valve are adjacent one another.

3. In a pneumatic driving machine, a casing having a pressure airreservoir, a cylinder in said casing exposed at one end to saidreservoir, an inlet valve for opening and closing communication betweensaid cylinder and said reservoir, a differential piston reciprocable insaid cylinder and forming therewith a pressure air return chamber formoving said piston on a return stroke towards said one end of saidcylinder, said casing having a passageway for supplying pressure airfrom said reservoir to said return chamber for normally maintaining thepiston near said one end of said cylinder ready to be driven on a powerstroke when said inlet valve is opened, said passageway including a portin said cylinder in constant comiunication with said pressure air returnchamber, said passageway having an inlet in constant communication withsaid reservoir and an outlet located adjacent said one end of saidcylinder and oriented relative to said inlet for directing a jet of thepressure fluid from said return chamber via said passageway past saidinlet and into said cylinder when the volume of the return chamber isreduced by movement of said piston on its driving stroke, saidpassageway extending along and exteriorly of said cylinder between saidport and said outlet thereof and being adapted for conducting saidpressure fluid from said return chamber to said outlet in isolatedrelation to the pressure air in said pressure air reservoir.

4. A pneumatically actuated fastener driving mechanism comprising acasing having a pressure air reservoir therein, a main cylinder havingan inlet end communicating with said reservoir, a power pistonreciprocable in said main cylinder, a second cylinder adjacent saidinlet end of said main cylinder, a valve piston reciprocable in saidsecond cylinder for opening and closing said inlet to control admittanceof pressure air from said reservoir to said main cylinder for drivingsaid power piston on a driving stroke, said valve piston having a firstpressure sur face partially exposed to pressure air in said reservoirwhen said valve piston is closed and fully exposed to said pressure airwhen said valve piston initially opens, said first pressure surfacebeing disposed to develop opening force on said valve piston, meansforming a restricted oriiice for supplying pressure air from saidreservoir to said second cylinder on the side of said valve pistonremote from said main cylinder for developing a closing force on saidvalve piston, normally closed trigger means operable for bleedingpressure air from said cylinder at a faster rate than it is suppliedthereto via said restricted orifice, an exhaust conduit communicatingwith said inlet end of said main cylinder and operably connected formovement with said valve piston, a closure on said casing having anexhaust passage normally communicating with atmosphere and with saidconduit, said closure being adapted to close communication between saidexhaust passage and said conduit when said valve piston'is open, saidconduit having a pressure surface exposed to pressure air in said maincylinder when said conduit is closed by said closure and adapted toco-operate with said remote side of said valve piston when said triggermeans is closed to provide an effective working area greater than andacting oppositely to said first pressure surface of said valve pistonfor developing sufficient force to initate cylinder-closing movement ofsaid valve piston.

5. The combination set forth in claim 4 wherein said means forming saidrestricted orifice comprises a portion of said valve piston having apassage therethrough with a restricted portion therein defining saidrestricted orifice, said valve piston passage communicating with saidsecond cylinder and with said fluid pressure chamber in all positions ofsaid valve piston.

6. In a pneumatic power unit of the type having a housing including anaccumulator chamber, a power cylinder having an opening at one endthereof communicating with said chamber and a piston movable in a powerstroke in said cylinder from a point of beginning adjacent said one end,a cylinder valve seating on an annular stop adjacent said one end of thecylinder and controlling communication between said chamber and saidcylinder, a valve-controlling piston operatively connected to saidcylinder valve, a valve cylinder in which said valve-controlling pistonis slidable to open and close said cylinder valve, means for supplyingpressure air to said chamber and to said valve cylinder on both sides ofsaid valve-controlling piston, a trigger valve for venting air from theside of said valve-controlling piston remote from said power unit pistonwhereby the pressure air on the other side thereof moves saidvalve-controlling piston to open said cylinder valve so as to admitaccumulated pressure air within said chamber through said inner end ofsaid power unit cylinder to drive said power unit piston in a powerstroke from said point of beginning; the combination therewith of meansforming an exhaust chamber communicating with atmosphere and defining apair of spaced walls disposed transverse to the axis of said valvecylinder and a cylindrical bore opening at one end thereof in one ofsaid walls coaxial with said valve cylinder and communicating therewithat the opposite end of said bore, an exhaust valve movable with saidcylinder valve and having an exhaust passage therein communicating withsaid power unit cylinder, said exhaust valve comprising a tubular memberfixed to said cylinder valve and having a cylindrical stem slidable insaid bore and a flanged end disposed in said exhaust chamber andradially spaced therefrom, said flanged end being adapted to axiallyabut the other of said walls of said exhaust chamber means when saidcylinder valve opens to thereby close communication between said exhaustpassage and said exhaust chamber, said flanged end moving out ofabutment with said other wall for opening said exhaust passage toatmosphere when said cylinder valve closes for exhausting spent pressureair from said power unit cylinder upon return of the power unit pistonto said point of beginning, said flanged end having a pressure surfaceconstantly exposed via said exhaust passage to pressure fluid in saidpower unit cylinder and disposed such that said pressure fluid actsthereon to initiate opening movement of said exhaust valve and closingmovement of said cylinder valve when said trigger valve is closed.

7. In a pneumatic fastener driving implement the combination comprisinga casing having a main cylinder open at one end, a valve cylinderadjacent said end of said main cylinder and a pressure air reservoircommunicating with said end of said main cylinder, a driving pistonreciprocable in said main cylinder, a valve piston reciprocable in saidvalve cylinder for opening and closing communication between saidreservoir and said main cylinder, an exhaust tube extending through aidvalve piston and movable therewith, means forming a fixed wall at an endof said valve cylinder remote from said main cylinder and slidablyreceiving said exhaust tube therethrough, said tube, valve cylinder,valve piston and wall defining a chamber therebetween, a restrictedpassageway adapted to admit pressure air from aid reservoir to saidchamber in all positions of said valve piston for urging it towardscylinder-closing position, trigger means for releasing pressure air fromsaid chamber at a faster rate than it is supplied thereto via saidrestricted passageway, said valve piston having a surface constantlyexposed ,to pressure air in said reservoir for opening said valve pistonwhen said trigger means is actuated to release pressure air from saidchamber, means including said tube forming an exhaust valve for closingexhaust of spent pressure air from said main cylinder via said tube inthe open position of said valve piston, said tube having a pressuresurface constantly exposed via said tube to pressure air in said maincylinder and adapted to develop a force on said tube for closing saidvalve piston when said trigger valve is actuated to prevent release ofpressure air from said chamber.

.8. The combination set forth in claim 7 wherein said driving pistonreciprocates between positions adjacent to and remote from the closedposition of said valve piston, said driving piston having a generallycup-shaped recess therein facing said valve piston, said valve pistonand said exhaust tube being adapted to project at least partially intosaid recess when said driving piston and said valve piston are adjacentone another to thereby restrict flow of pressure air from said reservoirinto said exhaust tube during initial opening movement of said valvepiston.

9. The combination set forth in claim 7 wherein said exhaust valve meansincludes a cap afiixed to said casing and adapted to form with said wallan exhaust chamher communicating with said tube and atmosphere, saidtube having annular flange means adapted to seat against said cap in theopen position of said valve piston for closing communication betweensaid tube and said exhaust chamber.

10. The combination set forth in claim 9 where-in said flange meanscomprises a flange having an end surface facing said cap and a seal ringthereon adapted for pres sure air sealing engagement with said cap andwherein said tube pressure surface comprises a portion of said endsurface of said flange disposed radially inwardly of said ring, saidring being adapted to space said flange surface from said cap duringengagement of the ring with the cap.

11. The combination set forth in claim 7 wherein said valve piston has aring of hard rubber or the like bonded thereto, said ring having atapered rim adapted for high contact pressure engagement with said endof said main cylinder in the closed position of said valve piston andfurther having a flat annular seating surface disposed radially inwardlyof said rim adapted for contacting engagement with said piston.

12. In a fastenenapplying machine the combination comprising a reservoirfor pres-sure fluid, a cylinder having an inlet port communicating withsaid reservoir, a piston reciprocable in said cylinder, a valve movableto open and close said inlet port, an exhaust tube movable with saidinlet valve and adapted to communicate .at opposite ends thereofrespectively with said cylinder and with atmosphere, mean for openingand closing the atmosphere end of said tube in response respectively toclosing and opening movement of said inlet valve, said tube having apressure surface exposed via the interior of said tube to pressure fluidin the cylinder when said tube is closed and disposed to develop anopening force on said tube, said inlet valve having a pressure surfaceexposed to reservoir pressure fluid for holding said inlet valve in openposition with a force greater than that developed by said tube pressuresurface and means for developing a force on said inlet valve additive tothe force of cylinder pressure fluid acting on said tube pressuresurface to thereby initiate opening movement of said tube and closingmovement of said inlet valve, said inlet valve and piston being disposedco-axially and moving oppositely relative to one another betweenpositions adjacent and remote from one another, said piston and saidinlet valve havin means movable therewith adapted to restrict flow ofpressure fluid from said reservoir into said exhaust tube when saidpiston and inlet valve are adjacent one another, said last-mentionedmeans comprising a projection extending axially from said piston intosaid tube with a pressure fluid flow restricting fit when said inletvalve and said piston are adjacent one another, said projection beingadapted to be Withdrawn from said tube when said inlet valve and saidpiston move oppositely relative to one another towards the remotepositions thereof.

- References Qited by the-Examiner UNITED STATES PATENTS 0,960,067 11/60Osborne 91-461 3,056,964 10/62 Beckrnan 91-4s1 SAMUEL LEVINE, Primary Eaminer; FRED E. ENGELTHALER, Examiner.

1. IN A FASTENERE-APLYING MACHINE THE COMBINATION COMPRISING A RESERVOIRFOR PRESSURE FLUID, A CYLINDER HAVING AN INLET PORT COMMUNICATING WITHSAID RESERVOIR, A PISTON RECIPROCABLE IN SAID CYLINDER, A VALVE MOVABLETO OPEN AND CLOSE SAID INLET PORT, AN EXHAUST TUBE MOVABLE WITH SAIDINLET VALVE AND ADAPTED TO COMMUNICATE AT OPPOSITE ENDS THEREOFRESPECTIVELY WITH SAID CYLINDER AND WITH ATMOSPHERE, MEANS FOR SLIDABLYGUIDING SAID TUBE AND FOR OPENING AND CLOSING THE ATMOSPHERE END OF SAIDTUBE IN REPONSE RESPECTIVELY TO CLOSING AND OPENING MOVEMENT OF SAIDINLET VALVE, SAID LAST-MENTIONED MEANS COMPRISING A SLEEVE ANDA CLOSURECAP DEFINING AN EXHAUST CHAMBER THEREBETWEEN COMMUNICATING WITHATMOSPHERE, SAID CAP DEFINING AN END WALL OF SAID EXHAUST CHAMBERDISPOSED PERPENDICULAR TO THE AXIS OF SAID TUBE AGAINST WHICH SAIDATMOSPHERE END OF THE TUBE AXIALLY ABUTS TO CLOSE THE SAME, SAID TUBEBEING SLIDABLY SUPPORTED IN SAID SLEEVE WITH SAID ATMOSPHERE END OF SAIDTUBE PROJECTING AXIALLY THEREFROM INTO SAID EXHAUST CHAMBER IN RADIALLYSPACED RELATION FROM THE RADIALLY SURROUNDING WALL OF SAID EXHAUSTCHAMBER ,SAID TUBE HAVING A PRESSURE SURFACE EXPOSED VIA THE INTERIOR OFSAID TUBE TO PRESSURE FLUID IN TE CYLINDER WHEN SAID TUBE IS CLOSED ANDDISPOSED TO DEVELOP AN OPENING FORCE ON SAID TUBE, SAID INLET VALVEHAVING PRESSURE SURFACE EXPOSED TO RESERVOIR PRESSURE FLUID FOR HOLDINGSAID INLET VALVE IN OPEN POSITION WITH A FORCE GREATER THAN THATDEVELOPED BY SAID TUBE PRESSURE SURFACE, AND MEANS FOR DEVELOPING AFORCE ON SAID INLET VALVE ADDITIVE TO THE FORCE OF CYLINDER PRESSUREFLUID ACTING ON SAID TUBE PRESSURE SURFACE TO THEREBY INITIATE OPENINGMOVEMENT OF SAID TUBE AND CLOSING MOVEMENT OF SAID INLET VALVE.